It is known to produce a high hydrogen product gas by reacting desulfurized hydrocarbons with water vapor on appropriate catalysts and then to separate the resulting product gas in a pressure swing adsorber to yield a high-purity hydrogen which can be utilized directly for hydrogenation.
Hydrogenation plants can operate the hydrogen pressures of 200 to 400 bar and at hydrogen temperatures of 250.degree. to 500.degree. C. and generally in the course of hydrogenation a high hydrogen gas is withdrawn from the hydrogenation process, is heated and is recycled to the hydrogenation process.
However, problems arise in the heating of hydrogen at high pressures and temperatures because of the high hydrogen permeability of the metals forming the pipelines and vessels which are traversed by the hydrogen-containing gas. In general, not only is hydrogen lost by penetration through the walls of steel or the like but the carbon content of the steel can combine with hydrogen to form methane and result in embrittlement or even destruction of the pipeline or the steel structures.
The high pressures which are involved preclude the use of steels of the low-carbon austenitic nickel-chromium type because such material would stand only light tensile stresses. It is for this reason that carbon steels in the form of ferritic alloys having a high carbon content must be used. Obviously, the additional carbon has a higher affinity to the alloying components than to hydrogen so that the formation of methane can be avoided. These alloying components can be chromium, molybdenum, tungsten or vanadium.
While this might appear to solve the problem because the resulting alloys are suitable for use in hydrogen lines and have been successful for this purpose, nevertheless problems are encountered because these alloys are subject to corrosion by sulphur during prolonged operation and to the extent that the corrosion may result in breakage of the tube to the detriment of the plant and operating person. The problem is especially severe because the highly explosive hydrogen is at a pressure of 200 to 400 bar.